Bollettino valanghe

West Slopes South

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
Open full map
Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You may not find much hazard first thing in the morning, but dangerous avalanche conditions could develop throughout the day as strong sunshine mixes with our cold winter snowpack. This may result in some hard-to-predict avalanches alongside more widespread Wet Loose slides. Make travel plans that give you plenty of options to avoid open sunny slopes and overhead hazard.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Temperatures should continue to climb Friday night into Saturday. Although some clouds may bookend the day, full sunshine is expected during the midday hours. You should anticipate Wet avalanche activity to increase throughout the day. The sunshine will first need to break down a crust from Friday before the surface starts to get wet and sticky. During this time period, you may see snow begin to shed from trees and rocks. Next, you will likely notice rollerballs and pinwheels on steep sun-exposed slopes. These are all precursors to Wet Loose avalanches. These slides will often start at a point and fan out as they descend, possibly growing large or triggering slabs in the process. When this scenario starts to unfold, your best bet will be to head to shadier slopes, keeping aware of overhead hazards.

    The strong March sun could result in other avalanche problems, some of which are more difficult to manage. See the discussion for details.

    (3/17/2023)

    Recent rollerball and Wet Loose avalanches on a steep sunny slope. Note how they originate at a point near rocks and trees.

    Photo: Rachel Gronvold

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    It has been not just cold and snowy recently, but also quite windy. This has resulted in Wind Slabs and large Cornices forming at mid to upper elevations. Although trending toward stubborn, most slabs have been identified as Hard Slabs, which are harder to predict and manage. They may not fail easily, but if they do, it will likely be without warning and could be large. (The same goes for Cornice failures which you can read more about in the discussion.) To identify wind-loaded areas, keep an eye out for features that look “fat” compared to the surrounding terrain. They’ll be most likely near ridgelines, on convex slopes, or the sides of confined gullies and can be found on multiple aspects. If you find yourself traveling over one, it should feel firm and possibly hollow.

    (3/17/2023)

    This slab avalanche failed this week when snow shed from the steep rocky terrain above. E, ~6000ft

    Photo: Dallas Glass

Avalanche Discussion

We have started to transition from an unseasonably cold and snowy period that has spanned the last several weeks into a relatively warm and sunny spell this weekend. On Friday, temperatures reached the 40s at multiple NWAC weather stations around the West South, but cool east winds helped to keep the snow mostly in place. Reported avalanches were generally small D1-D1.5 Wet Loose slides. Saturday should be warmer than Friday and we are forecasted to lose the cool breeze. We’re hedging on a larger wet avalanche cycle occurring in the afternoon hours.

The recent cold snow is still going through its settling process but we’re going to throw it into a state of confusion with this warm-up. Weird avalanches can occur during periods like this and they can be difficult to capture using the North American public danger scale. There is some growing concern for very large (D3) avalanches failing deeper in the snowpack. We have had a number of these lower likelihood, high consequence slides around the Cascades this week, including multiple in within the West South zone. The most common characteristics are that they appear to fail in high-elevation terrain that is likely wind-loaded and possibly involved a cornice failure. This includes multiple slides at Mount St. Helens and one in Mount Rainier National Park.

We do not think you will be able to trigger one of these larger avalanches as a traveler. However, the threat of blocks of snow such as cornices or glides failing and triggering slides on the slopes below is in the back of our minds. Take these hard-to-predict scenarios into consideration when making your trip plans. Think about avoiding large alpine features as well as the terrain in their runout zone, especially during periods of intense sunshine.

The upper snowpack around the West South zone is aspect dependent but generally well-settled. On slopes that see direct sunshine, expect to find a firm sun crust in the morning before sunshine is able to soften the surface throughout the day. On the more shaded side of the dial, you can still find layered cold dry snow with pockets of weak grains. You’ll likely see signs of recent wind effect as you ascend in elevation on most aspects. In some areas, the wind effect will be mixed with recent solar influence.

Regioni coperte